Question

我搜索过并发现：How to check if a value already exists in the database in Android。我遇到的问题是，当输入的值与数据库中已有的值匹配时，toast永远不显示并且数据仍然输入数据库。我看过有关使用UNIQUE来确保数据不重复的帖子，但它不适用于我需要做的事情。我试过if（entries.contains（checkDuplicates）== false）和if（！entries.equals（checkDuplicates）），并且也得到了相同的结果。我知道这很简单，我缺少或不理解。有人会帮助我，并指出正确的方向吗？

    private void saveState() {

    Calendar calendar = Calendar.getInstance();
    SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
    eventDate = sdf.format(calendar.getTime());

    String date = eventDate;
    String event = eventTitle.getText().toString();
    String empID = fiveAndTwo.getText().toString();

    /**
     * CRUD Operations
     * */
    // Inserting entries to DB

    // Reading all contacts
    Log.d("Reading: ", "Reading all entries..");

    List<EventEntries> entries = db.getAllEntries();

    for (EventEntries ee : entries) {
        String log = "Id: " + ee.getID() + " Date: " + ee.getDate() + " Event Name: " + ee.getEvent() + " Emp ID: " + ee.getempID();

        // Writing entries to log
        Log.d("Entry: ", log);


    }

    String checkDuplicates =  date + event + empID;

    if (!entries.contains(checkDuplicates)) {

        Log.d("Insert: ", "Inserting ..");

        db.addEntry(new EventEntries(date, event, empID));
        String logEntry = "Date: " + date + " Event Name: " + event + " Emp ID: " + empID;
        Log.d("Entered to DB:", logEntry);

    } else {

        Toast.makeText(this,"Employee has already been scanned for this event.", Toast.LENGTH_SHORT).show();

    }
}

编辑：我得到了它的工作。这是我做的：

    private void saveState() {

    Calendar calendar = Calendar.getInstance();
    SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
    eventDate = sdf.format(calendar.getTime());

    String date = eventDate;
    String event = eventTitle.getText().toString();
    String empID = fiveAndTwo.getText().toString();

    /**
     * CRUD Operations
     * */

    // Reading all entries
    Log.d("Reading: ", "Reading all entries..");

    List<EventEntries> entries = db.getAllEntries();

    for (EventEntries ee : entries) {
        String log = "Id: " + ee.getID() + " Date: " + ee.getDate() + " Event Name: " + ee.getEvent() + " Emp ID: " + ee.getempID();

        // Writing entries to log
        Log.d("Entry: ", log);

    }

    EventEntries checkDuplicates = new EventEntries(date, event, empID);

    if (!entries.contains(checkDuplicates)) {

        Toast.makeText(this,"Successfully entered.", Toast.LENGTH_SHORT).show();

        // Inserting entries to DB
        Log.d("Insert: ", "Inserting ..");
        db.addEntry(new EventEntries(date, event, empID));
        String logEntry = "Date: " + date + " Event Name: " + event + " Emp ID: " + empID;
        Log.d("Entered to DB:", logEntry);


    } else  {

        empAlert();

    }
}

以下是我添加到EventEntries类的内容：

    @Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((_date == null) ? 0 : _date.hashCode());
    result = prime * result + ((_empID == null) ? 0 : _empID.hashCode());
    result = prime * result + ((_event == null) ? 0 : _event.hashCode());
    return result;
}

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    EventEntries other = (EventEntries) obj;
    if (_date == null) {
        if (other._date != null)
            return false;
    } else if (!_date.equals(other._date))
        return false;
    if (_empID == null) {
        if (other._empID != null)
            return false;
    } else if (!_empID.equals(other._empID))
        return false;
    if (_event == null) {
        if (other._event != null)
            return false;
    } else if (!_event.equals(other._event))
        return false;
    return true;
}

Answer 1

entries.contains(checkDuplicates)始终返回false，因为entries是EventEntries对象的列表，checkDuplicates是String。您应该使用entries.contains对象作为参数调用EventEntries。

还有一件事：

// assuming entries is not empty
EventEntries first = entries.get(0);
entries.contains(first);  // --> this is TRUE

// create a dupe of "first"
EventEntries firstDupe = new EventEntries(.....);
entries.contains(firstDupe);  // --> in *general* this is FALSE

一般来说，第二种情况是错误的。如果在EventEntries类中覆盖equals方法以使first.equals(firstDupe)返回true，则可以如此。只有这样，第二个例子才会返回true。

以下是一个示例实现：

public boolean equals(Object obj) {
    if (obj instanceof EventEntries) {
        EventEntries other = (EventEntries)obj;
        if (date.equals(other.date) && event.equals(other.event)
            && empID == other.empID) {
            return true;
        }
    }
    return false;
}

（必要时调整。）

Answer 2

替换：

String checkDuplicates = date + event + empID;

使用：

EventEntries checkDuplicates = new EventEntries(date, event, empID);

检查列表是否包含多个值android

2 个答案: